Here's how we can tell:
* Iamb: An iamb is a metrical foot consisting of an unstressed syllable followed by a stressed syllable (da-DUM).
* Pentameter: Pentameter refers to five metrical feet per line.
Let's break down the line:
* you (unstressed) could (stressed) not (unstressed) love (stressed)
* the (unstressed) Dear (stressed) so (unstressed) much (stressed)
* Loved (stressed) hon (unstressed) or (stressed) more (stressed)
You can see that each line has five iambs, making it iambic pentameter. This meter is very common in English poetry, especially in sonnets and other traditional forms.